There are many previously known devices for positioning tools, welding guns and the like for mass production machining and assembly operations. Some previously known lift and carry workpiece transfer mechanisms have used a so called Watts linkage drive to raise and lower the workpieces.
A Watts linkage is a three link kinematic mechanism which has three long links pivotally connected together at adjacent ends with the remaining ends of two of the links pivoted about spaced apart and fixed pivot points. The links are constructed and arranged in a geometry that produces an essentially linear reciprocating motion of the center of the middle link. It is well understood that in a Watts linkage the links must be relatively long to produce this linear motion. Further, because the links do not move in a true straight line, a Watts linkage is not driven or powered by an actuator producing straight line or rectihinear motion.
The prior device disclosed in U.S. Pat. No. 5,216,930, utilizes a modified Watts linkage powered by an actuator having a straight line motion. While this device has been effective at powering the work arm with a linear actuator, it provides shock adsorption at only one end of the path of the work arm movement. Thus, at the end of the work arm movement where no shock absorption is provided, stresses can result on the system from the abrupt stoppage of the work arm which effects the durability and reliability of the system.